So MC keeps Draitor around because he really wants another player with him in this world of NPCs, but also because the MC probably isn't strong enough to resist the author's influence yet and Draitor is an employee of the company so he is there to help the scenario work. If he wants that human connection then he should have picked up the hero and started training him too... but maybe that's for later. I guess the Goddess (main author for the novelization system) doesn't want the "game" to end, because if MC killed off the last boss (who might be a GM or someone similar tasked with managing the demons but can't break out of the scenario himself) then the story ends, game over, we gotta write and release an expansion pack.
Delicate as an orchid, fair as a cherry blossom, the personification of feminine grace and also... a dude. Tall as a willow, slender as a reed, a dude. Radiant in shrine vestments, dude. The sun dips low in a rosy sky, cicadas buzz, is a dude.
I have a feeling that Diina is the Goddess. Well at least the Goddess' Avatar. Remember how Lufasu felt that there was something wrong with Diina's reasoning even after she confessed to being Venus? Well maybe she isn't a "test gamer" but the Goddess in disguise. I mean isn't it strange that Diina is the only other "player"? Especially since Lufasu's player was intentionally called by the Goddess. So that leaves two options: The Goddess intentionally brought Diina into the game world for some reason or Diina IS the Goddess. This is also supported by her current double agency between Lufasu and The Demon King.
@tonicwalter You're right it does sound really obvious but given the fact that Diina was already caught in one of her lies it's not. Well, we'll see I guess.